Mesityl oxide has been oxidized with air over various catalysts, including V.sub.2 0.sub.5, with molar ratios of O.sub.2 to mesityl oxide of 1:1 to 2:1 and temperatures of 418-608.degree.C. to produce dimethylfuran (U.S. Pat. No. 3,228,966). If any citraconic anhydride was produced it apparently was not recognized.
Mesityl oxide has been oxidized in the liquid phase with air over a cobalt catalyst at 70.degree.-120.degree.C. Vanadium salts were said to be useful as a replacement for the cobalt catalyst. The only identified product was .alpha.-methyl-.beta.-acetylacrylic acid (U.S. Pat. No. 2,443,8l8).
Citraconic anhydride has been made by the acetylation and pyrolysis of citramalic acid (Kunichika et al., Kyoto University Institute for Chemical Research Bulletin, 44, No. 3, pp. 221-225 (1966)).